Within CircleCI, there are two different methods of enabling status checks for your projects.
Organization Level Status Updates: https://app.circleci.com/settings/organization/github/<org>/vcs
You can manage which projects utilize GitHub checks by clicking "Manage GitHub Checks"Project Level Status Updates: https://app.circleci.com/settings/project/github/<org>/<project>/advanced
If you have disabled one of these options, and are still receiving checks, it is likely that the other option is enabled.
Checks prefixed with ci/circleci are from the project level status updates using the GitHub Status API, and will show "CircleCI (@circleci) generated this status" when hovering over the CircleCI logo.
The checks without a prefix are from the CircleCI Checks GitHub integration, and will show "@circleci-checks generated this status"
Additional resources
You can read more about enabling/disabling GitHub checks within our documentation here: https://circleci.com/docs/guides/integration/enable-checks/